1. Field of the Invention
The present invention relates to technology for correcting three dimensional distortion of an image, to a high accuracy.
2. Description of the Related Art
Nowadays, in the financial world such as of banking, with a goal of improving the efficiency of input operations, a technique which uses a non contact type image-pickup device such as a CCD (charge coupled device) or a digital camera, for inputting a paper record or paper document at high speed and conveniently is being put to practical use. When the non contact type image-pickup device is used, then compared to a contact type image-pickup device such as an image scanner, the convenience of being able to write etc. on the paper face even during image input, and being able to effect high speed image input while viewing the paper, can be enjoyed.
On the other hand, in the image input by the non contact type image-pickup device, there exists a perspective transformation distortion attributable to the non contact image input, and image distortion attributable to bending of the paper face curved surface. Furthermore, even with an image which is input by the contact type image-pickup device, if this is one where the paper face of a thick book is imaged, since the paper face becomes a curved surface, then similarly there exists an image distortion. Therefore, in the input images by the use of the image-pickup device, technology for correcting these image distortions becomes indispensable. Therefore, the present applicants has proposed, as disclosed in Japanese Unexamined Patent Publication No. 2002-150280, a technique for estimating the paper face curved surface using as a clue the distortion of a two dimensional outline of the paper face extracted from the image, and correcting the distortion of the image.
However, in this proposed technique, the types of distortion which are the object of correction are limited, and also it is necessary to specify these types, so that for actual images where the types of distortion are diverse, application of the technique must become difficult. Furthermore, when the whole of the paper face does not appear in the image, the outline thereof cannot be extracted, and hence various restrictions are imposed on the image correction.